A portable telephone system, such as a second-generation digital cordless telephone (CT-2) system, includes telepoint sites each having multiple transceivers. These transceivers allow persons using portable telephones (cordless telephone handsets) to access the public switched telephone network (PSTN) when in range of a telepoint. Each of the individual telepoint transceivers provide a particular channel of operation (at a different frequency) which can be used by a handset in order to communicate through the CT-2 system to the PSTN.
CT-2 systems typically operate between 864.150 MHz and 868.050 MHz, and can provide up to a theoretical maximum of 40 communication channels per telepoint (base-site), with each telepoint channel having 100 MHz channel spacing. The center frequency for the 40 channels can be calculated as: 864.050 MHz+(0.100.times.n) MHz, where "n" is the channel number lying in the range of 1 to 40. In practice, since adjacent channels are not used due to selectivity constraints, a maximum of 20 channels is usually the practical limit. Most telepoint's usually have no more than 12-14 channels due to in-band interference and intermodulation problems in high density areas (e.g., a high-rise building or downtown area having more telepoints close to each other). As the number of channels in a telepoint increases, approaching the 20 channel practical maximum, the chances of not providing a good quality communication channel (communication link) increases tremendously due to greater chance for interference caused by adjacent channels, intermodulation, etc.
Presently, communication channels in a CT-2 system are assigned by determining which channels are available and assigning one of the available channels. The present, CT-2 channel assignment technique unfortunately does not provide telepoint users the best available (optimum) channel in terms of providing the communication channel having the least likelihood of being affected by interference or affecting other channels with interference(e.g., by adjacent or intermodulation channels, etc.).
A need thus exists for a method of assigning communication channels in a multi-channel system which can provide for the optimum channel available at any given point in time from an interference standpoint. Such an assignment method would in turn provide for higher capacity levels (more channels available) for the system with the same or less chances of interference.